A stabilizer in the stabilizer device functions as a spring, restraining horizontal oscillation of an automobile body by warping a left arm part and a right arm part in mutually opposing directions, and by contorting a torsion part, when mutually opposing phases in the up and down direction are applied to the suspension mechanisms on the left and right, when an automobile having such a stabilizer device passes through a curve. Conventionally, the stabilizer has been fixed to the automobile body by fastening a bracket to an automobile body side with a bolt via a rubber bushing arranged on the stabilizer.
However, due to a load generated by centrifugal force when passing through a curve, the torsion part and the bushing may each resist the frictional force of the other, so that they become misaligned with each other. These misaligned parts will not be returned to their original positions even in the case in which a centrifugal force is generated in an opposite direction or in the case in which the automobile then goes straight, and thus the parts would be maintained misaligned from the original positions. Therefore, there may be a problem in which anti-roll effects by the stabilizer cannot be obtained, a problem in which excessive load may be applied on a stabilink fastened on both ends of the stabilizer, and there is a likely problem that the stabilizer may interfere at a circumferential part.
To prevent the bushing from being misaligned, an aluminum ring or an iron ring has been swaged as a misalignment preventing member. As the misalignment preventing member, one member for each of the left and right, in total two members, are used per one stabilizer. On the other hand, as a method for preventing the bushing from being misaligned, there is a method in which a rubber bushing itself is directly fixed to the torsion part by an adhesive or by a heat-curing process.
In a process for production of a hollow stabilizer device having the aluminum ring as the misalignment preventing member, first, a forming process in which an electric resistance welded tube cut into a predetermined length is formed into a shape of a stabilizer by a cold-working is performed, next, a heat treatment process in which the half-finished product of the stabilizer is heat-treated by, for example, quenching or tempering is performed, next, shot-peening in which shot is impinged on the half-finished product of the stabilizer is performed, and next, a coating process in which the half-finished product of the stabilizer is coated is performed. After that, the aluminum ring consisting of half portions or two pieces is swaged to obtain the misalignment preventing member.
In addition, in a process for production of a hollow stabilizer device having the iron ring as the misalignment preventing member, first, an arm part is formed by a bending process of an electric resistance welded tube cut into predetermined length, next, the electric resistance welded tube is bent and is inserted into an iron ring formed into a C-shape, and next, a process in which a flattened part and an attachment hole for attaching a stabilink are formed at an edge part of the arm part by forging or the like is performed. After that, the iron ring is swaged and a coating process is performed.
On the other hand, in the process for fixing a rubber bushing, the rubber bushing is integrally formed at the torsion part of the stabilizer by direct injection, and it is then hardened by a heat curing process. As cited references concerning these techniques, Japanese Unexamined Patent Application Publication Nos. 2001-163026 and 2001-165127 may be mentioned.
However, since it is a method for fixing in which an aluminum ring consisting of half portions or two pieces are swaged to the torsion part, the aluminum ring has a connecting part which is a structural weak point. Because of this connecting part, the strength of the aluminum ring is low. Therefore, in the case in which a load is applied to the aluminum ring, the swaged form may be easily broken. Therefore, the fixing strength of the aluminum ring may be easily deteriorated, and fixed positions of the stabilizer at left and right parts of the automobile may become unbalanced. When the automobile passes through a curve, the effects that the stabilizer originally had cannot be sufficiently obtained. As a result, it is not a stabilizer device having sufficient reliability.
In addition, since the aluminum ring is swaged and fixed to the half finished product of the stabilizer after coating, the ring is fixed to the stabilizer via coating. Therefore, it may depend on the coating strength, which is a degree of adhering between the half-finished product of the stabilizer and the coating. Therefore, in the case in which the original coating strength is not obtained, the misalignment preventing member may move with the coating, the fixing strength of which the misalignment preventing member originally has cannot be obtained, and the function as the misalignment preventing member cannot be obtained. As a result, it is not a stabilizer device having sufficient reliability. Furthermore, in the case in which the misalignment preventing member is an aluminum ring or an iron ring, it is heavier than the misalignment preventing member made of resin. Therefore, weight reduction of the stabilizer device cannot be promoted.
In addition, since deformation resistance of the iron ring is higher than that of the aluminum ring, the iron ring is formed into a circular shape so as to be swaged easily. Therefore, it is necessary that the torsion part be inserted into the ring before the flattened part and the attaching hole for attaching the stabilink are formed at the edge part of the arm part by forging or the like. That is, it is necessary that the electric resistance welded tube be inserted into the iron ring after bending the electric resistance welded tube and before coating of the half-finished product of the stabilizer. Therefore, handling is difficult since the process for forming the flattened part and attaching hole must be performed while the iron ring is maintained so as not to drop off or fall without swaging it.
Furthermore, since the rubber bushing requires the heat curing process, the process for production becomes complicated and is expensive. In addition, in the direct injection of rubber, part of the rubber forms burrs and projects from a gap between a shoulder part of a stabilizer and a grip part of a mold supporting the shoulder part of the stabilizer. For example, it has been demonstrated that the burrs are formed even in the case in which the gap is about 0.2 mm. Therefore, a process for removing the burrs is necessary, incurring additional costs.